Abstract: A transmitted signal and a received signal are combined and the combination is expected to determine whether or not a target signal is present. Either the transmitted signal or the received signal is combined with an auxiliary signal containing a range of frequencies corresponding to an anticipated Doppler shift, so that an output of the combined transmitted and received signal will be present only if a target signal exhibiting a Doppler shift within the anticipated range is present. The auxiliary signal preferably comprises finite-duration signal portions of different types so as to provide a substantially uniform frequency response throughout the selected range.

Abstract: A transmitted signal and a received signal are combined and the combination is expected to determine whether or not a target signal is present. Either the transmitted signal or the received signal is combined with an auxiliary signal containing a range of frequencies corresponding to an anticipated Doppler shift, so that an output of the combined transmitted and received signal will be present only if a target signal exhibiting a Doppler shift within the anticipated range is present. The auxiliary signal preferably comprises finite-duration signal portions of different types so as to provide a substantially uniform frequency response throughout the selected range.

Abstract: A non-repeating sequence of numbers having a substantially uniform distribution is obtained from a shift register whose contents are shifted, with the shifted digits being replaced by digits from a continuous sequence. The contents of the shift register are also replaced by their complement in dependence for the value of the most significant bit, so that the operations performed on the contents are represented by a tent map, thereby providing uniform distribution of the numbers. A randomising subsystem can be used to convert the output sequence into a random sequence.

Abstract: A signal can be analysed to determine statistical characteristics indicative of, for example, the predictability or time reversibility of the signal. The signal is examined to locate events corresponding to the crossing of predetermined levels with predetermined slopes. Multiple versions of the signal are combined, the versions being shifted with respect to each other by amounts corresponding to the spacings of the detected events. The shape of the resulting representation provides statistical information regarding the signal.

Abstract: A receiver is tuned into a multicarrier signal first by performing fine tuning control in the time domain, and then determining a coarse frequency offset to adjust the subcarrier to which the receiver is tuned. The coarse frequency offset is determined by summing the powers of a predetermined set of subcarriers associated with one frequency offset, repeating this for other frequency offsets, and determining whether the largest sum has a predetermined relationship to the other sums. Discrimination is improved by disregarding the largest of the powers when determining the sum. Preferably, the sums are integrated over multiple symbol periods, and the speed of locking-in is increased by terminating the operation when the predetermined relationship has been reached.

Abstract: The delay between a first signal and a second signal is evaluated by deriving from the first signal substantially aperiodic events, possibly by using a zero-crossing detector on a random signal, and using these events to define respective segments of the second signal. The segments are combined, e.g., by averaging, to derive a waveform which includes a feature representing coincidences of parts of the second signal associated with the derived events. The delay is determined from the position within the waveform of this feature.

Abstract: A transmitted signal and a received signal are combined and the combination is expected to determine whether or not a target signal is present. Either the transmitted signal or the received signal is combined with an auxiliary signal containing a range of frequencies corresponding to an anticipated Doppler shift, so that an output of the combined transmitted and received signal will be present only if a target signal exhibiting a Doppler shift within the anticipated range is present. The auxiliary signal preferably comprises finite-duration signal portions of different types so as to provide a substantially uniform frequency response throughout the selected range.